Electrode-active material, lithium-ion battery, method for detecting discharge state of electrode-active material, and method for manufacturing electrode-active material

Abstract

An electrode-active material, a lithium-ion battery, and a method for detecting a discharge state of an electrode-active material that make it possible to realize high load characteristics, high cycle characteristics, and high energy density, have a high degree of safety and stability, and make it possible to easily detect the state of a late stage of discharge are disclosed. The electrode-active material is obtained by coating the surface of a particle containing Li w A x DO 4 with a coating layer containing Li y E z GO 4 . In a discharge curve of the electrode-active material, a second region which follows a first region showing a substantially constant discharge potential and shows a drop in a discharge potential includes a third region in which a rate of change in a discharge potential is lower than an average rate of change in a discharge potential of the second region.

1 . An electrode-active material comprising:
 a particle composed of Li w A x DO 4  wherein A represents 1 or 2 kinds selected from the group consisting of Mn and Co, D represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<w≦4, and 0<x≦1.5; and   a coating layer formed on the particle, containing Li y E z GO 4  wherein E represents either Fe or Fe and Ni, G represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<y≦2, and 0<z≦1.5,   wherein in a discharge curve of the electrode-active material, a second region which follows a first region showing a substantially constant discharge potential and shows a drop in a discharge potential includes a third region in which a rate of change in a discharge potential is lower than an average rate of change in a discharge potential of the second region.   
     
     
         2 . The electrode-active material according to  claim 1 ,
 wherein a capacity at 60° C. of the third region is from 1/20 to ⅓ of a maximum value of a discharge capacity.   
     
     
         3 . The electrode-active material according to  claim 2 ,
 wherein a reaction potential at 60° C. of the third region is from 3.0 V to 3.8 V.   
     
     
         4 . A lithium-ion battery having a positive electrode that contains the electrode-active material according to  claim 1 . 
     
     
         5 . A method for detecting a discharge state of an electrode-active material comprising a particle composed of Li w A x DO 4  wherein A represents 1 or 2 kinds selected from the group consisting of Mn and Co, D represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<w≦4, and 0<x≦1.5; and a coating layer formed on the particle, containing Li y E z GO 4  wherein E represents either Fe or Fe and Ni, G represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<y≦2, and 0<z≦1.5,
 wherein in a discharge curve of the electrode-active material, within a second region which follows a first region showing a substantially constant discharge potential and shows a drop in a discharge potential, a third region in which a rate of change in a discharge potential is lower than an average rate of change in a discharge potential of the second region is detected. 
 
     
     
         6 . An electrode-active material comprising a particle composed of Li w A x DO 4  wherein A represents 1 or 2 kinds selected from the group consisting of Mn and Co, D represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<w≦4, and 0 21  x≦1.5; and a coating layer formed on the particle, composed of a complex consisting of Li y E z GO 4  wherein E represents either Fe or Fe and Ni, G represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<y≦2, and 0<z≦1.5, and a carbonaceous electron-conducting material,
 wherein in a discharge curve of the electrode-active material, a second region which follows a first region showing a substantially constant discharge potential and shows a drop in a discharge potential includes a third region in which a rate of change in a discharge potential is lower than an average rate of change in a discharge potential of the second region. 
 
     
     
         7 . The electrode-active material according to  claim 6 ,
 wherein a capacity at 60° C. of the third region is from 1/20 to ⅓ of a maximum value of a discharge capacity.   
     
     
         8 . The electrode-active material according to  claim 7 ,
 wherein a reaction potential at 60° C. of the third region is from 3.0 V to 3.8 V.   
     
     
         9 . A lithium-ion battery having a positive electrode that contains the electrode-active material according to  claim 6 . 
     
     
         10 . A method for manufacturing an electrode-active material, comprising:
 a step of forming a mixture by mixing a particle composed of Li w A x DO 4  wherein A represents 1 or 2 kinds selected from the group consisting of Mn and Co, D represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<w≦4, and 0<x≦1.5, with an Li source, an E source wherein E represents either Fe or Fe and Ni, a G source wherein G represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, and an organic compound;   a step of then forming a dried material by drying the mixture; and   a step of then generating a carbonaceous electron-conducting material by carbonizing the organic compound by performing thermal treatment on the dried material in a non-oxidative atmosphere, such that a coating layer composed of a complex consisting of Li y E z GO 4  wherein E represents either Fe or Fe and Ni, G represents 1, 2, or more kinds selected from the group consisting of P, Si, and S, 0<y≦2, and 0<z≦1.5; and the carbonaceous electron-conducting material is generated on the surface of the particle composed of Li w A x DO 4 .   
     
     
         11 . The method for manufacturing an electrode-active material according to  claim 10 ,
 wherein the Li source, the E source, the G source, and the organic compound are mixed together such that these become a uniform liquid phase.